196 ELECTRO-PHYSIOLOGY CHAP. 



of ascending and opening of descending currents, because in 

 the first case the katelectrotonic, in the second the anelectrotonic 

 part of the nerve communicated directly with the spinal column ; 

 the leg connected with the nerve, on the other hand, twitched 

 according to the law of contraction only with the two opposite 

 stimuli. With medium currents, all four stimuli were reflexly 

 responded to, as previously pointed out by Matteucci. Setschenow 

 and Hallsten (46) have since investigated the same question, 

 arriving at essentially the same results. 



The consequences of exciting mixed centripetal nerves, which 

 consist of antagonistically working fibres, e.g. the vagus, are 

 much more complicated. Griitzner discovered that the closure 

 and passage of constant ascending currents, and in a less degree 

 the opening of descending currents, had an inhibitory, expiratory 

 effect upon respiration, while opening of ascending and closure 

 of descending currents remained ineffective. Langendorff and 

 Oldag (7) have recently submitted these facts to more accurate 

 investigation, finding that an ascending constant current, sent 

 into the central end of the vagus, " in all cases influences 

 respiration in the expiratory direction ; i.e. it either induces a 

 longer expiratory arrest, or retards the breathing by inducing 

 expiratory pauses." And this is the case not merely at the 

 moment of closure, but throughout prolonged passage of current. 

 Breaking the current in most cases induces a visible inspiratory 

 effect, expressed either in a deepening of inspiration, or in a short 

 inspiratory stoppage. The closure and passage of the descend- 

 ing constant current were always found by Langendorff and 

 Oldag to be less effective than those of the ascending current, 

 and that in an antagonistic sense, i.e. inspiratory ; while opening 

 the circuit again produces an inspiratory standstill. 



" Inhibition of respiration (expiratory) is therefore produced by 

 closure of the ascending and opening of the descending constant 

 current ; excitation of respiration (inspiratory) by opening of the 

 ascending and closure of the descending current." 



The same (expiratory) action as with ascending constant 

 currents may also be produced on thoroughly narcotised animals 

 by interrupted constant currents of uniform direction, especially 

 where the frequency of interruption is small, and the closure of 

 prolonged duration. Inspiratory effects, on the other hand, not only 

 appear with closure of descending persistent currents, but still 



